Method And Reactor For Biomass Pyrolytic Conversion

ABSTRACT

A method and apparatus performing high temperature fast pyrolysis of dry biomass are described. High yield of gases with medium caloric value and low tar content are claimed. Passing electric current through the mixture of biomass with conductive particles in the stirred bed inside the reactor provides the intensive direct heating of the biomass in the pyrolytic reactor.

FIELD OF THE INVENTION

The present invention relates to biomass conversion into energy. Moreparticular, the present invention relates to biomass pyrolyticconversion to fuels; mainly in gaseous form.

BACKGROUND OF THE INVENTION

Biomass resources can be used as bioenergy. Biomass in general is thebiodegradable fraction of products, waste and residues from agriculture(including vegetal and animal substances), forestry and relatedindustries, as well as the biodegradable fraction of industrial andmunicipal waste. Usage of biomass resources is developed in three ways:biomass for heating purposes (bio-heating); biomass for electricityproduction (bio-electricity); and biomass for transport fuels(transportation biofuels).

As mentioned, many types of biomass are available for conversion intoenergy. The efficiency of converting biomass into energy is determinedby specific characteristics of the applied biomass technology. Theprofitability of the applied technology is strongly determined by theamount of the biomass available. One of the problems associated withbiomass usage is the relatively high cost of biomass transportation thatreduces the profitability.

At present, the following technologies are developed and applied forbiomass conversion into electric energy:

-   -   Firing in boilers (Fluid Beds as a rule) with generation of        steam and its utilization in Rankin cycle; application of this        method is limited by the necessity of gathering big amounts of        biomass.    -   Gasification of biomass and further firing of the gases in gas        turbines or engines; low calorific value of the generated fuel        gases seriously limits its efficiency.    -   Pyrolysis of the biomass. This method, if successful, provides        gaseous or liquid fuels with high calorific value for power        generation and seems to be especially convenient for small power        units (˜0.5 MW) destined for in situ heat generation.

Pyrolysis of biomass is taught in the art and is the scope of thepresent invention due to the high caloric value of the product and themassive possibility for in situ use that eliminates the biomasstransportation cost. As an example, U.S. Pat. No. 5,387,321 “Apparatusfor Waste Pyrolysis” filed in 1992 by Holland describes a pyrolyserwhere a pulverulent material is heated by electromagnetic microwaves andtransfers its thermal energy to the biomass. The use of microwaves iscostly and requires, for the amount of energy required, sophisticatedelectrical installations. Another example disclosed in U.S. Pat. No.5,618,321 “Pyrolysis Gasifier with Inner Sleeve Member” by Beierle etal. describes a pyrolyser wherein a paddle distributes the biomass on avertical fluid bed. The heat required is supplied by burning in situpart of the biomass by controlled introduction of air, a hose nitrogendilutes the final fuel-gas product.

A unique pyrolyser is described in U.S. Pat. No. 6,048,374 “Process andDevice for Pyrolysis of Feedstock” by Green. The patent describes apyrolyser where an auger moves, mixes and improves the heating of thebiomass. The heat required is supplied by burning part of the solidresidue in a combustion chamber in a zone situated below the pyrolyser,and the gases from the combustion dilute the pyrolysis gas. U.S. Pat.No. 4,308,103 “Apparatus for the Pyrolysis of Comminuted SolidCarbonizable Materials” filed in 1980 by Rotter describes a horizontalcylindrical pyrolyser with a shaft having mixing paddles. The pyrolyseris heated by firing fuel in a bracketed mantel around the pyrolyser.

The available solutions that are brought herein as references as well asother solutions fail to provide an efficient pyrolyser for biomassconversion into energy. Most of those solutions do not deal with in situreactors and therefore, do not solve the high costs of biomasstransportation involved in biomass-to-energy conversion.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a reactor forbiomass pyrolytic conversion to energy such as electric power and heatgeneration.

It is another object of the present invention to provide a reactor forbiomass pyrolytic conversion to energy that is in situ and eliminate thehigh cost involved in biomass transportation.

It is yet another object of the present invention to provide a methodfor biomass pyrolytic conversion to energy that is both effective andeconomical.

It is therefore provided in accordance with a preferred embodiment ofthe present invention a method for pyrolytic processing of biomasscomprising:

-   -   feeding crushed dried biomass into a pyrolytic reactor        comprising a body, a revolving shaft, and electricity conductive        particles;    -   mixing the dried biomass and said conductive particles;    -   applying a current to the electricity conductive particles so as        to allow the conductive particles as well as the biomass to heat        up;    -   partially cooling vapors-gaseous products created by pyrolysis        and producing fuel-gas;    -   whereby a pyrolysis process is realized within the pyrolytic        reactor and fuels for power generation production.

Furthermore in accordance with another preferred embodiment of thepresent invention, the biomass within said pyrolytic reactor is heatedat a high heating rate up to a temperature between 700 and 1000° C.

Furthermore in accordance with another preferred embodiment of thepresent invention, said temperature is between 750 and 850° C.

Furthermore in accordance with another preferred embodiment of thepresent invention, the biomass is any type of dry solid waste biomass.

Furthermore in accordance with another preferred embodiment of thepresent invention, said biomass is selected from a group of biomassessuch as olive husks, wood, forest and agricultural residues such asbagasse, coconut shell, corn stalks, wheat straw, rice husk and ricestraw, dried sludge from water treatments.

It is also provided in accordance with yet another preferred embodimentof the present invention, a pyrolytic reactor for biomass processingcomprising:

-   -   a cylindrical body;    -   a revolving shaft within said cylindrical body, wherein said        shaft is adapted to mix the biomass;    -   at least one raw material feeder provided to said cylindrical        body;    -   at least one product coke discharge system;    -   at least one pipe for volatile products evacuation;    -   conductive particles provided within said cylindrical body;    -   Whereby electric current that is supplied through said shaft and        through said cylindrical body is transmitted through said        conductive particles so as to allow sufficient heating of the        conductive particles as well as the biomass that is mixed with        them while pyrolysis of the biomass occurs.

Furthermore in accordance with another preferred embodiment of thepresent invention, said cylindrical body is equipped with a chamber foradditional (secondary) pyrolysis.

BRIEF DESCRIPTION OF THE FIGURES

In order to better understand the present invention and appreciate itspractical applications, the following Figures are attached andreferenced herein. Like components are denoted by like referencenumerals.

It should be noted that the figures are given as examples and preferredembodiments only and in no way limit the scope of the present inventionas defined in the appending Description and Claims.

FIG. 1 a illustrates a cross sectional side view of a reactor-pyrolyserin accordance with a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION AND FIGURES

The method for converting biomass to available energy described in thepresent invention is based on very rapid and intensive heating of thebiomass within a specially designed reactor or pyrolyser. Rapid heatingis achieved by mixing the biomass with conductive solid particlesthrough which an electric current is passed.

It was found unexpectedly that the application of a low voltage ofelectric current through a steered bead of conductive particles allowsfast heating of this bed. When introducing in this heated bed ofparticles dry organic waste particles, the electric heating goes on andan efficient pyrolysis is obtained.

The explanation of the efficiency of the pyrolysis is due to both theJoel effect on the bed of steered particles and due to the localmicro-sparkles of high intensity that occur between the particles.

The method of the present invention enables conversion of differenttypes of biomass into fuels; mainly in gaseous form.

According to one aspect of the present invention, the method forgenerating fuels from biomass involves an initial stage in which adedicated reactor as will be comprehensively explained herein after isfilled to about 50% of its volume with conductive particles. Examples ofconductive particles can be coke, metal particles etc. The conductiveparticles are heated by passing an electric current through them. Thecurrent passes between two electrodes and preferably the reactor bodyand the stirrer and through the conductive particles within the reactor.The particles are heated up to about 850 degrees Celsius.

Then, dried and crushed biomass is added continuously. These biomassparticles are mixed with the conductive particles in a way that preventsthe decrease of the total reactor content conductivity, and are rapidlyheated. The conductivity of the mixture is controlled by the ratiobetween the biomass and the conductive particles.

The stirred biomass is decomposed in the reactor under combined actionof high temperature and electricity, yielding gases, vapors and coke.

Primary volatiles created by the pyrolysis process such as gases,organic vapors and steam undergo a secondary pyrolysis on the surface ofthe conductive particles all along the reactor.

Primary organic vapors that contain large amounts of oxygen in theirmolecules are decomposed by the secondary pyrolysis and are convertedmainly into fuel gases. The presence of primary pyrogenic water (steam)reduces the entrainment of “fly” coke through secondary pyrolysis.

Primary pyrogenic water (steam) reacts with organic substances, e.g.according to the following gasifying reaction:

C_(m)H_(n) +mH₂O<->mCO+m+n/2H₂.

This secondary pyrolytic gasification decreases the amount of organicvapors and steam, and increases the amount of fuel gas produced.

Reference is now made to FIG. 1 illustrating a side view of areactor-pyrolyser in accordance with a preferred embodiment of thepresent invention. The reactor comprises a horizontal cylindrical body 1having a chamber 10 for secondary pyrolysis of primary volatileproducts. A horizontal revolving shaft 5 is provided within cylindricalbody for mixing the materials. Shaft 5 holding at least one of aplurality of paddles 6 also passes the processed material through thecylindrical body and provides intensive mixing. At least one system forraw material feeding 7 is provided on top of cylindrical body 1 and atleast one solid discharge system 8 is provided in the bottom part of thebody. A pipe for volatile products evacuation 16 is provided at the endof chamber 10. The inner face of the side covers 2 and part of the shaft5 are coated with insulation, preferably ceramics, in order to supplythe necessary electric insulation.

Seal systems 3 are provided at the shaft outlets.

Electric current is supplied by electrical connections 13 through shaft5 and its mixing paddles 6 that form one branch of the circuit, andthrough the reactor's body 1, which is the second branch of the circuit.The circuit is closed by the electro-conductive particles 12 that fill apart of the reactor's volume. Both branches are electrically connectedto a low voltage high intensity source 15.

An apparatus similar to the reactor shown in FIG. 1 was built andtested. Table 1 shows typical compositions of gaseous products producedaccording to the method of the present invention. LHV stands for lowheating value. The results represent an average value of multipleexperiments.

It should be mentioned that any type of biomass can be used andconverted into energy using the method of the present invention. Theapparatus of the present invention is especially designed for olive oilproduction waste; however, any other type of biomass is covered by thescope of the present invention.

It should be clear that the description of the embodiments and attachedFigures set forth in this specification serves only for a betterunderstanding of the invention, without limiting its scope as covered bythe following Claims.

It should also be clear that a person skilled in the art, after readingthe present specification can make adjustments or amendments to theattached Figures and above described embodiments that would still becovered by the following Claims.

TABLE 1 Typical Composition of the Gaseous Products (in mass %,nitrogen* and water free basis). Experiments Component LHV(kcal/kg)mass, % LHV(kcal/kg) Methane CH₄ 11,948 5.74 686 Ethylene C₂H₄ 11,2763.25 366 Ethane C₂H₆ 11,351 1.94 220 CO₂ — 5.79 0 CO 2,415 56.9 1374 H₂28,679 6.43 1844 O₂ — 1.59 N₂ — 7.66 0 Total LHV average 4,491 (kcal/kg)Total LHV average 18.8 (MJ/kg) *The fuel-gas is supposed to contain verylittle amounts of nitrogen, from air introduced by the waste granules orfrom organic nitrogen in the waste.

1. A method for pyrolytic processing of biomass comprising: feedingcrushed dried biomass into a pyrolytic reactor comprising a body, arevolving shaft, and electricity conductive particles; mixing the driedbiomass and said conductive particles; applying a current to theelectricity conductive particles so as to allow the conductive particlesas well as the biomass to heat up; partially cooling vapors-gaseousproducts created by pyrolysis and producing fuel-gas; whereby apyrolysis process is realized within the pyrolytic reactor and fuels forpower generation production.
 2. The method as claimed in claim 1,wherein the biomass within said pyrolytic reactor is heated at a highheating rate up to a temperature between 700 and 1000° C.
 3. The methodas claimed in claim 2, wherein said temperature is between 750 and 850°C.
 4. The method as claimed in claim 1, wherein the biomass is any typeof dry solid waste biomass.
 5. The method as claimed in claim 4, whereinsaid biomass is selected from a group of biomasses such as olive husks,wood, forest and agricultural residues such as bagasse, coconut shell,corn stalks, wheat straw, rice husk and rice straw, dried sludge fromwater treatments.
 6. A pyrolytic reactor for biomass processingcomprising: a cylindrical body; a revolving shaft within saidcylindrical body, wherein said shaft is adapted to mix the biomass; atleast one raw material feeder provided to said cylindrical body; atleast one product coke discharge system; at least one pipe for volatileproducts evacuation; conductive particles provided within saidcylindrical body; Whereby electric current that is supplied through saidshaft and through said cylindrical body is transmitted through saidconductive particles so as to allow sufficient heating of the conductiveparticles as well as the biomass that is mixed with them while pyrolysisof the biomass occurs.
 7. The reactor as claimed in claim 8, whereinsaid cylindrical body is equipped with a chamber for additional(secondary) pyrolysis.